The present invention concerns an amplifier used in high frequency (hereinafter abbreviated as xe2x80x9cHFxe2x80x9d), particularly, in the range of 5-13 GHz, more specifically, in the range of 9-12 GHz, in which electromagnetic coupling between the input circuit and the output circuit of the amplifier is prevented.
Conventional HF-amplifiers have the structure, as shown in FIG. 1 and FIG. 2, of a metal case 1 consisting of a box type container 11 and a lid 12, an amplifying element 2 installed on a dielectric, insulating board 5 in the case, and leads 3 and 4 connected to the input circuit and the output circuit of the amplifying element and extending outside through both one end wall 16 and the opposite end wall 17 of the case.
In this type of HP amplifier it is inevitable that electromagnetic coupling occurs between the input circuit and the output circuit, and there are some problems due to the coupling, such as difficulty in achieving desired gain as well as decrease in fidelity of amplification. Thus, prevention of coupling (hereinafter referred to as xe2x80x9cdecouplingxe2x80x9d) is an important technical problem in this kind of HF amplifier.
With the attempt to solve this problem the inventor tried disposing an electromagnetic wave-absorbing material in the metal case consisting of a box type container and a lid, and at the bottom of which an amplifying element is installed on a dielectric, insulating board. Positions to dispose the eletromagnetic absorbing material may be inside both the side walls, inside both the end walls and inside the lid or on the ceiling. The first trial was made on the ceiling. As the electromagnetic wave-absorbing materials there were used the following three kinds of sheets comprising a rubber or plastic as the matrix material and carbon powder, ferrite powder or a soft magnetic metal powder dispersed therein.
The survey was carried out at first on the effect of inner dimensions of the metal case, i.e., width xe2x80x9caxe2x80x9d, height xe2x80x9cbxe2x80x9d and length xe2x80x9ccxe2x80x9d as shwon in FIG. 4, on the coupling, and then on the thickness of the dielectric, insulating board 5 on which the amplifying element 2 is installed.
The following facts were found:
1) As the electromagnetic wave-absorbing materials those made by dispersing a soft magnetic metal powder in a rubber matrix and rolling to form sheets, which the inventor has been developing, exhibit good results;
2) In such a small case as the width xe2x80x9caxe2x80x9d is 12 mm or less, as seen from the graph of FIG. 5, coupling is not a problem;
3) Regarding the height xe2x80x9cbxe2x80x9d, in case of carbon powder dispersed sheets, the larger the height is, the less the coupling is; In case of ferrite powder dispersed sheets, little influence of the height was appreciated; and in case of soft magnetic metal powder-disperses sheets, a smaller height is favorable from the view to prevent coupling;
4) With respect to the distance between port 2 and port 3 in FIG. 4, as seen from the graph of FIG. 7, in any case of different electromagnetic wave-absorbing material longer port distance between the input circuit and the output circuit will result in decreased coupling; and
5) As to the thickness of the dielectric, insulating board 5 on which the amplifying element 2 is installed, as seen from the graph of FIG. 8, the thinner the board is, the more effective the decoupling is. However, because the insulating board must have certain mechanical strength, about 0.6 mm will be a practical lower limit.
In the HF amplifier in which an electromagnetic wave-absorbing material containing dispersed soft magnetic metal powder on the ceiling of the case the electromagnetic wave which may cause coupling between the input circuit and the output circuit is absorbed by the absorbing material and thus, coupling will be effectively decreased. For example, in the frequency range of 9-12 GHz, amplification of 25 dB can be achieved without decrease of gain caused by coupling.
In order to enable amplification of higher gain without suffering from coupling the inventor continued development, and found the following facts:
6) The decoupling effect is different depending on the positions of disposing the electromagnetic wave-absorbing material in the cases of the HF amplifier;
7) The electromagnetic wave-absorbing sheets prepared by dispersing a soft magnetic metal powder in a rubber matrix have optimum ranges of combination of the powder filling-rate and the thickness of the sheets for the electromagnetic wave-absorption performance; and
8) In the case where the above electromagnetic wave-absorbing sheets are prepared by rolling the absorption characteristics are different depending on the relation between the rolling direction of the sheet and the direction of signal propagation.
The object of the present invention is to utilize the above-described novel knowledge obtained by the inventor and to provide an HF amplifier to be used in a frequency range of, typically, 9-12 GHz, which can achieve high gain without suffering from coupling between the input circuit and the output circuit, and to which no influence is given on the amplification fidelity.
The HF amplifier of this invention has the same components as those of the conventional HF amplifiers, as shown in FIG. 1 and FIG. 2. The components are a metal case 1 consisting of a box type container 11 and a lid 12, an amplifying element 2 installed on a dielectric, insulating board 5 at the bottom of the case, and leads 3 and 4 connected to the input circuit and the output circuit of the amplifying element and extending outside through both one end wall and the opposite end wall of the case. The present HF amplifier is characterized in that an electromagnetic wave-absorbing sheet 7 or sheets are disposed inside of at least one of both the side walls 13 and 14, the ceiling 15, and both the end walls 16 and 17 so as to prevent electromagnetic coupling between the input circuit and the output circuit. In the example of FIG. 3, the electromagnetic wave-absorbing sheet 7 is disposed on the ceiling 15.